This invention relates in general to air filters and particularly to an improved two stage air breather filter especially intended for use on large engines operated in a dirt and dust laden environment.
If particulate matter should enter the intake system of an engine, such as a highly sophisticated diesel engine, over a period of time it will cause serious damage and result in considerable down time. It is therefore, important to increase both the efficiency of the filter and its dirt separating capacity, while at the same time, not making the filter unduly complex and/or requiring the use of expensive filter elements.
Air breather filters of the type with which the present invention is concerned are disclosed in U.S. Pat. Nos. 2,230,453 and 3,508,383, 3,853,518 and 4,243,397.
U.S. Pat. No. 2,230,453 concerns an air filter of the liquid reservoir type wherein liquid from the reservoir is entrained in the incoming air, and such air is then successively passed through a double vortex cyclone chamber and a filter element. The term "double vortex cyclone" is used in this patent to designate a form of mechanical air-cleaning device which is composed of a conical casing open at its smaller lower end and provided at its larger upper end with an axial outlet and an outlying swirl-producing inlet. This structure compels the air flowing through the casing to form an outer vortex as it travels spirally from the inlet toward the smaller end and then to reverse its direction and form an inner vortex as it travels spirally toward the axial outlet.
While an air filter of the type disclosed in U.S. Pat. No. 2,230,453 may be effective in many applications, it is obviously of complex and expensive construction. Moreover, in many applications, it may not be desireable to introduce oil into the incoming air, as is the case with this device.
In U.S. Pat. No. 3,508,383, there is disclosed an air filter having a deflector as an end cap of the filter unit. A flange extending outwardly from the end cap is provided with blades which engage the housing and cause the air to swirl within the housing to thus separate the heavy dust particles from the air by the swirling action before the air passes through the filter media. This filter is also of complex construction having foraminous inner and outer tubes, utilizes a relatively expensive tubular pleated filter element, and does not have a second stage of particulate filtration.
U.S. Pat. No. 3,853,518 teaches an air filter having a vortex tube precleaner or a cyclone separator precleaner, and a dry filter element surrounding the inertial separator which acts as a final filter. The cyclonic action takes place within a conically-shaped separator formed within the filter casing.
U.S. Pat. No. 4,243,397 discloses a filter having a pleated filter element supported within a double wall cone. The pleated filter element, safety sleeve assembly and outer liner are meant to be sold in a replacement kit, while the inner metal liner is retained and reused during subsequent air cleaning operations.
Such prior art filters, while serving the basic purpose for which they were designed, are either of complex design and therefore expensive to fabricate, or do not have the filtering efficiency required in particularly harsh operating environments. Moreover, the cost for the replacement filter elements used in such prior art filters is expensive.